Differences In Blood-flow Patterns Of The Carotid Artery Between Two Exercise Modalities At Three Intensities

Abstract

Endothelial shear stress (ESS), frictional force produced by red blood cells on endothelial cells, helps to maintain endothelial homeostasis, and help to determine blood flow patterns. Purpose: This study seeks to determine exercise-induced blood flow patterns in the carotid artery during different exercise modalities (back squat and treadmill running) at 3 different intensities. Methods: Fourteen participants (7 males and 7 females) participated in a repeated measures study design. Three sessions were performed to obtain baseline measurements, 1-repetition maximum back squat test (1RM Squat), and treadmill maximum oxygen uptake test (VO2max). Two more sessions, for squat and treadmill, were randomized within a week after the baseline measurements. Squat intensities selected: low = 45% 1RM, moderate = 65% 1RM, and high = 85% 1RM. Running intensities were selected using blood lactate levels: low = 0-2 mmol/L, moderate = 2-4 mmol/L, and high >4.0 mmol/L from the VO2max test. Blood flow patterns of the carotid artery (diameter and blood flow velocity) and presence of turbulence determined by calculation of Reynolds number (Re), were obtained using ultrasound imaging and Doppler. Data analysis used a 2-way repeated-measures ANOVA, with Holm-Bonferroni post-hoc analysis to determine pairwise differences between modalities and intensity. Statistical significance was set at α = 0.05. Results: There were main effects and interaction between intensity and exercise modalities (p < 0.05) for ESS. Pairwise comparisons showed difference in moderate (p < 0.05) and high (p < 0.05) intensity in both modalities (Figure 1A) compared to low intensity. Similarly, there was a main effect of exercise intensity (p < 0.05) for Re. Pairwise comparisons indicate significant difference (p < 0.05) in high intensity in both modalities (Figure 1B) compared to low intensity. Conclusion: Results indicated turbulent blood flow patterns across all intensities and modalities; however, high intensity treadmill yields greater turbulent blood flow. Furthermore, ESS increases linearly as intensity increases, with greater magnitude in moderate and high intensity treadmill. Clinicians should be aware of differences in carotid artery hemodynamics at different exercise intensities and modes to prescribe better exercise interventions.